Our invention is in the field of magnetic disk drives such as, typically, those of the Winchester type wherein the transducer head "flies" or is airborne at a small spacing from the magnetic recording surface of a hard disk during the transfer (reading or writing) of data therewith. More particularly, our invention concerns a mechanism in such magnetic disk apparatus for controlling the radial position of the transducer head on the recording disk.
In the Winchester disk drive, as is well known, the magnetic transducer head or heads are aerodynamically maintained out of contact with the recording surface or surfaces as the disk or disks rotate at a sufficiently high speed for data transfer. As the disk speed drops upon completion of data transfer, each head lands on the associated disk surface and stays in contact therewith until the disk speed builds up to a predetermined degree at the start of the next run of data transfer. Accordingly, if the disk drive is subjected to shocks or vibrations while each head is thus maintained in contact with the associated disk, the disk surface has been easy to be ruined by the hand sliding therefore.
A solution, though incomplete, to this problem is found in U.S. Pat. No. 4,593,329 issued to Hayakawa and assigned to the assignee of our present application. This patent takes advantages of the fact that not all the surface of the magnetic disk but a limited annular part thereof is actually used for data storage. Thus the disk surface has "noneffective" annular regions, where no data is to be stored, that are located both radially inwardly and outwardly of the effective data storage region. Hayakawa suggests to position the head on one of the noneffective surface regions of the disk when the disk is out of rotation, or in rotation at less than a prescribed speed, thereby avoiding the contact of the head with the effective surface region of the disk. However, the head is not locked in that standby position according to this prior art.
We have found that it presents no serious problem in one type of disk drive, but is a fatal defect in another, to leave the head unlocked in the standby position as in the noted prior art. There are two well known methods of transporting the head from track to track on the magnetic disk. One is to employ a rotary actuator, typically a stepping motor, in combination with a mechanism for translating its rotation into the linear motion of the head in a radial direction of the disk. The other is to use an angular actuator such as a voice coil motor for directly driving a pivoted head arm carrying the head.
In the first mentioned type of head transport mechanism, the rotary to linear converter interposed between the motor and the head carriage serves to mechanically hold the head in the standby position to some extent in the face of mechanical vibrations applied to the apparatus. Although the rotor of the stepping motor is susceptible to displacement when it is not energized with a holding current, no significant displacement of the head will normally result by reason of the interposition of the motion translating mechanism.
However, in the second recited type of head transport mechanisms, the angular motion of the voice coil motor is transmitted directly to the head arm. As the motor coil is displaced, so is the head on the head arm. Consequently, left unlocked on the noneffective surface region of the disk according to the prior art, the head driven by this type of head transport mechanism has been easy to move onto the effective surface region of the disk. This disadvantage becomes all the more serious because the coil of the voice coil motor is particularly susceptible to displacement because of the motor construction itself.